The present invention relates to a liquid crystal display. Particularly, this invention relates to the structure of a transparent electrode layer formed on a transparent substrate of a liquid crystal display.
Liquid crystal projectors have recently been used, for example, for presentation of new products using images created by computer-graphics and projected onto a screen and in home theater in which moving pictures are projected onto a large screen.
As displaying devices used for liquid crystal projectors, reflective liquid crystal displays have gotten a lot of attention for high intensity and high resolution because of high aperture ratio at high pixel density.
FIG. 1 is a sectional view showing a known liquid crystal display.
A liquid crystal display 100 is provided with a transparent electrode substrate 110 and a substrate 120 of integrated circuitry and a liquid crystal layer 130 interposed therebetween. The substrate 120 is called an IC-substrate hereinafter.
The transparent electrode substrate 110 consists of a transparent electrode layer 112 and a first orientation film 113 stacked under a transparent glass substrate 111.
The IC-substrate 120 consists of an active-matrix driver 122, a pixel electrode layer 123 and a second orientation film 124 stacked on a silicon substrate 121.
In operation, a linearly-polarized reading light beam I is incident from the transparent electrode substrate 110 side to reach the pixel electrode layer 123 through the transparent electrode substrate 110 and the liquid crystal layer 130.
A light beam reflected on the pixel electrode layer 123 passes through the liquid crystal layer 130 in the direction reversal of incidence and is emitted from the transparent electrode substrate 110. The emitted reading light beam I is projected onto a screen via a projection lens (both not shown) for displaying an image thereon while it is optically modulated to be a projection beam O in accordance with a video signal in the liquid crystal layer 130.
Liquid crystal projectors are usually provided with a discharge-type light source of high intensity, such as, a metal halide lamp or a ultra high-pressure mercury lamp of high emission efficiency. These lamps contain mercury as an emission triggering gas. They generate strong emission lines of 440, 540 and 580 nm in an emission spectrum for mercury in a visible radiation range.
The transparent electrode layer 112 of the transparent electrode substrate 110 is made of a transparent conductive film such as ITO (Indium Tin Oxide) of high reflectivity.
Thus, there is a big difference in reflectivity at the interfaces between the transparent electrode layer 112 and the liquid crystal layer 130.
This causes reflection, on the interfaces, of some beam components of the light beam which have been reflected on the pixel electrode layer 123. Moreover, interference fringes could occur on a projected image due to interference between emission lines of specific wavelength involved in the projection beam O and a reflected beam R that is the emission line reflected on the interfaces when the reading light beam I carries the strong emission lines described above.
U.S. Pat. No. 5,570,213 discloses a multi-layer anti-reflection film formed on a transparent electrode layer for restricting reflection on the interfaces between the transparent electrode layer and a liquid crystal layer, thus controlling occurrence of interference fringes.
FIG. 2 is a sectional view showing a transparent electrode substrate disclosed in U.S. Pat. No. 5,570,213.
Elements shown in FIG. 2 that are the same as or analogous to elements in the reflective liquid crystal display in FIG. 1 are referenced by the same reference numbers and will not be explained.
A transparent electrode substrate 110 is provided with a multi-layer anti-reflection film 117 formed on a transparent electrode film 114 on a transparent glass substrate 111. The multi-layer anti-reflection film 117 consists of low-reflectance dielectric films 115 and high-reflectance dielectric films 116, totally four films laminated by turns. A transparent electrode layer 112 consists of the transparent electrode film 114 and the multi-layer anti-reflection film 117.
Optical film thickness of each of the low- and high-reflectance dielectric films 115 and 116 is decided by simulation so that the multi-layer anti-reflection film 117 has an optimum anti-reflecting function against emission lines of specific wavelength among those generated by a light source.
The multi-layer anti-reflection film 117 that consists of the low- and high-reflectance dielectric films 115 and 116 is, however, not a conductive material, and hence the anti-reflection film 117 is charged, at its surface, with ionized impurities, etc., that have been involved in the liquid crystal layer 130 due to d. c. voltage application for driving the liquid crystals.
Charges such as ionized impurities remain on the antireflection film 117 even if the liquid crystal layer 130 is turned off. This causes a situation as if it is still turned on, that is, a still image or a fixed pattern of image generated while the liquid crystals have been driven remains on the layer 130, which is called image sticking.
A purpose of the present invention is to provide a liquid crystal display of high image quality with restricted interference fringes and no image sticking even if employing a light source of high emission efficiency for generating strong emission lines.
The present invention provides a liquid crystal display including: a first substrate on which a pixel electrode layer is formed; a second transparent electrode substrate on which a transparent electrode layer is formed, the transparent electrode layer having a first transparent film, a transparent electrode film, a second transparent non-conductive film and a transparent conductive film, the films being laminated on the transparent electrode substrate in order; and a liquid crystal layer interposed between the first and the second substrates so that the pixel electrode layer and the transparent conductive film face each others wherein the transparent conductive film has an extended portion that reaches the transparent electrode film so that the transparent conductive film is electrically coupled to the transparent electrode film via the extended portion.
Moreover, the present invention provides a liquid crystal display including: a first substrate on which a pixel electrode layer is formed; a second transparent electrode substrate on which a transparent electrode layer is formed, the transparent electrode layer having a first transparent film, a transparent electrode film and a second transparent film, the films being laminated on the transparent electrode substrate in order; and a liquid crystal layer interposed between the first and the second substrates so that the pixel electrode layer and the second transparent film face each other, wherein the second transparent film has resistivity low enough to transfer charges to the transparent electrode film.
Furthermore, the present invention provides a method of forming a transparent electrode layer on a transparent substrate of a liquid crystal display in which a liquid crystal layer is interposed between the transparent electrode layer and a pixel electrode layer. A first transparent film and a transparent electrode film are formed on the transparent substrate in order by vacuum deposition at respective specific thickness. A specific region of the transparent electrode film is masked with resists. A second transparent non-conductive film is formed on the transparent electrode film having the masked specific region. The resists are removed from the masked specific region. A transparent conductive film is formed on the second transparent non-conductive film and on the resist-removed specific region so that the transparent conductive film reaches the transparent electrode film via the specific region.
Moreover, the present invention provides a method of forming a transparent electrode layer on a transparent substrate of a liquid crystal display. A first transparent film and a transparent electrode film are formed on the transparent substrate in order by vacuum deposition at respective specific thickness. A second transparent film is formed on the transparent electrode film by ion plating at room temperature.